Related art techniques of a cap having an unjust-unsealing preventing function (pilfer-proof function) include a technique disclosed in Japanese Examined Utility Model Registration Application Publication No. 1995-12294.
This related art exhibits the pilfer-proof function in such a way that: a pour spout that is opened and closed by a hinged upper lid is formed; an inner lid made of a metal plate for covering to close the opening of a bottle mouth cylinder is joined to a lid main body detachably screwed on the bottle mouth cylinder to form a lid; a break line is formed at the lower end of a skirted wall of the lid main body; the skirted wall is divided into an upper main section and a lower pilfer-proof base section; the main section and the pilfer-proof base section are connected with a plurality of breakable ribs; and a locking protrusion is provided on the inner face of the pilfer-proof base section, which is locked from below across a ring-shaped locking jaw of the bottle mouth cylinder.
In this related art, the lid main body must be unscrewed from the bottle mouth cylinder when the inner lid is removed to unseal the bottle first; however, the rib is broken by the unscrewing of the lid main body from the bottle mouth cylinder, so that the pilfer-proof base section is separated from the main body to drop to the lower part of the bottle mouth cylinder. Accordingly, with the lid main body mounted on the bottle mouth cylinder after the inner lid has been removed, the pilfer-proof base section is apart from the mounted lid main body; thus, it can be determined that the bottle has already been unsealed at the sight of this separated state.